Abstract. The binary phase diagram of Ag2SO4 -BaSO4 system is proposed using X-ray powder diffraction, thermal analysis (DTA/DSC), manning electron microscopy, and electrical conductivity results. About 5 mol-% BaSO4 is soluble in ~-AgeSO 4. The two-phase (Ag2SO4+BaSO4) mixture exists for 10-90 tool-% of BaSO4 between room temperature and 578 ~ An eutectic of 578 ~ exists of the composition 70Ag2SO4 + 30BaSO4 The conductivity maximum within the solid solubility limits is due to the generation of extrinsic vacancies and lattice expansion as a result of partial substitution of the bigger aliovalent Ba 2 § for the Ag+-ions. The eutectic composition shows the maximum conductivity in the entire binary system due to the minimum in grain size, thereby providing a maximum surface ion conducting path. About 1 min response time of the sensor based on using the eutectic composition, as solid electrolyte, is much shorter than that of the sensor with pure AgzSO4.

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